Keithley 237 Service Manual

SECTION
3
Maintenance
38A Analog
Control Lines
Control
lines,
managed
by
the
source/measure
control
1er,
are
used
to
drive
the
various relays,
switching
FETs
and
analog
switches
associated with analog
circuitry
op
eration.
That
is, an
appropriate
voltage
level present
on
a
control
line will
cause
the
respective
switch
to dose or
open.
These
controllines
(located
on schematic
236426,
pagel)
drive relay
coils,
gates
of
switching FETs,
and inputs of
analog
switches. The following
summarizes
the
nominal
voltage levels
that should
be
present
on the
control
lines
to drive
these switching
devices.
NOTE
To
check voltage
levels
on
control lines,
refer
ence
the
measurement
to floating
common.
CAUTION
On
the
Model 236/237,
remove
the
ground
link
from
output
common
when using
chas
sis
grounded
equipment
to make
measure
ments
referenced
to
floating
ground.
Other
wise,
erroneous
measurements
or possible
instrument
damage may
result.
Relay
Drive
K8, K9,
KlO,
KIl and
K12;
OV =
relay
switch
closed
+5V = relay
switch
open
Kl, K3, K4,
K5,
K6, K7 and
K15;
OV = relay
switch
open
+5V = relay
switch
closed
FET Switch
Drive
N-channel
FET;
OV = switch
closed
(on)
—15V =
switch
open
(0ff)
P-channel
FET;
OV = switch
closed
(on)
+15V =
switch
open (off)
Analog
Switch
Drive
(U45,
U48
and
U49)
OV = switch
closed
+5V = switch
open
Other control
lines
that
are not used
to
drive
switching
devices are
described
as
follows:
COMPLIANCE
Used
for compliance
detection.
When
the Model
236/237
is in
compliance, this
controlline
is
at
0V. Otherwise,
+5V
is on this line.
POLARITY
Used
to
provide
the
appropriate
10V ref
erence
for the clamping circuits.
When
the instrument
is
programmed
for a positive
(+)
output,
this control
line is
at nominally
+10V.
When
programmed for a negative
(—)
output,
this
line is at nominally
—10V.
lOOmA
RANGE BIAS —
Used
to select the
appropriate
current
limit
to
the output
stage.
With
the instrument
on
the lOOmA
range (source or
measure),
this control
line is
at +5V.
On the other
current
ranges this line is
at 0V.
38.5 Analog
Switching
Tables
3-3 through
3-8
provide
the switching
states
of
most of the analog circuit
switching devices
for the van-
ous openating
conditions.
Current
Ranging
Table
3-4 lists
the switches
that
ane
closed for
each of
the nine curnent ranges.
This table
ap
plies
to both sounce
and measure curnent
ranges. Notice
that on the 1 nA
nange
none of the
cunnent
nange nelays are
closed.
Relays
Range
Closed
Range Switches
Closed
lOOmA
K8 Q5-Q9, Q37,
Q38
lOmA
K9 U45A, Ql0, QIl
lmA
K9 U45A,Q12,Q13
lOOpA
K9 U45A,
Q4, Q14
lOiiA
K9
U45A,
Q4
ljiA
KlO
U45A,Q4
lOOnA
K1l
U45A,Q4
lOnA
K12 U45A,
Q4
lnA
U45A,Q4
Table 3-4,
Analog Switching
Current Ranging
3-14

Keithley 237 Specifications

General

Brand	Keithley
Model	237
Category	Measuring Instruments
Language	English